36 
MR, W. K. PARKER ON THE STRUCTURE AND 
All the structures are now rapidly passing into their permanent form, although 
the individuals are, at this time, very small. 
The endocranium is here of the typical form ; a flat-bottomed “ barge,” with one 
large anterior, and two small posterior membranous spaces in the “ deck.” 
The larger lateral expansions behind are connected with the lesser lateral expan¬ 
sions in front, by an elegant bow of cartilage, the pterygo-palatine (pg., e.pa.) ; the 
hinder expansions are caused by the impaction of the ear-masses into the sides of 
the skull, and the expansions in front are due to the nasal growths; from the open 
spaces between, on each side, the eye-balls have been removed. 
The two pairs of ossifications in the endocranium, the prootics and the ex-occipitals 
( pr.o ., e.o.), are considerably larger than in the last stages ; the hinder pair have quite 
encircled the twin passage for the 9th and 10th nerves ; a trace of the notochord ( nc.) 
still remains. 
There is no gh’dle-bone yet; thus, with the exception of the “ centres ” just men¬ 
tioned, the endocranium is a “ chondrocranium.” The form of the contents of the 
ear-capsule is well seen through the semi-transparent cartilage, and the form and 
extent of the originally separate nasal roofs, as distinguished from the pre-cerebral 
region of the cranium, are well seen. Also below (fig. 7), the manner in which the 
“ intertrabecula ” has filled in the space between the “ cornua trabeculae,” and the 
sub-division of the root of the “ horns ” into a pro-rliinal hook, and a subnasal outer 
angle ( p.rh ., s.n.l.), are clearly seen; also the divisions of the upper labials (fig. 6, 
u.l l .a.l~.), and their relation to the outer nostril (e.n.). 
The “ ethmo-palatine ” bar (e.pa.) is lobate; the pre-palatine is spiked, and the 
post-palatine is a gently lessening bar, which with the pre-palatine region in front 
and pterygoid region (pg.) behind, forms a most elegant subocular “ bow.” 
Behind, this bowed bar ends in three lobes ; the quadrate with its reniform condyle 
(q.c.) running outwards, and downwards, and backwards; the “pedicle” (pd.) pedate, 
with a flat inturned facet below; and the “ otic process ” above, clamping the outer 
and front end of the “ tegmen tympani.” 
For articulation with the quadrate we see the cylindroidal condyle of the mandible 
(fig. 8, ar.c.); the under and inner face of the long arched rod is invested by the 
“articulare ” (ar.) nearly to the fore end ; the “ dentary” (d.) runs along the distal half 
on the outside, and it is grafting itself, near its lower end on the lower labial, which 
is not quite confluent with the mandibular rod (mk.), and which is itself' ossifying, to 
become the “ mento-Meckelian ” bone (- m.mJc .). 
The obliquely semi-oval stapes (figs. 7 and 10, st.) has now wedged in, between its 
fore margin and the ear-capsule, the proximal end of the “ columella ” (epi-hyal element). 
This structure is not yet finished, and has a subdivision in it very rarely seen in 
adults, but which is normal in certain fishes (e.g., the “ Acipenseridse ”). 
These two parts are, morphologically, the proximal or “ hyomandibular,” and the distal, 
